There is an increasing demand for eye and face protection for people who participate in sports and other activities that can potentially damage the eyes or other facial structures. Eye injuries (sometimes leading to loss of vision) can occur in sports such as hockey and football in which objects (such as sticks, pucks, or another player's elbows or fingers) can strike a participant's eye or face with destructive velocity and force. Protective shields are also used for a variety of non-sports related tasks, such as mowing lawns or hammering nails, to help prevent inadvertent projectiles from injuring the eye or face. An increased awareness of the potentially infectious nature of body fluids has also prompted many health care professionals to wear protective eyewear or face shields when treating patients, to avoid accidental infections from blood, saliva or other fluids splattered into the eye or on other mucus membranes.
One drawback to the use of protective face shields is that shields can distort the wearer's vision. Early face shields were merely a flat sheet of plastic bent into an arcuate shape to conform to the facial contour. However such a shield causes significant optical distortion that can be distracting to the wearer, and cause serious performance problem in persons who require precise visual input, such as athletes, pilots and surgeons.
The prior art is replete with examples of efforts to overcome optical distortion in protective eyewear. Rayton's U.S. Pat. No. 1,741,536 (issued in 1929 to Bausch & Lomb) discloses a protective goggle in which the front and back surfaces of the lenses were defined by two spheres having offset centers. An optical centerline (optical axis) through the centers of the spheres is spaced from, and oriented parallel to, a direct straight ahead line of sight. This optical configuration provides a tapered lens, in which the lens thickness gradually decreases symmetrically from the optical center toward the edges. Maintaining the line of sight parallel to the optical axis helps neutralize the distortion that would otherwise be caused by wrapping the lenses laterally with respect to the eye.
The problem of distortion in a face shield was also addressed in U.S. Pat. No. 4,271,538 (the Montesi patent), which disclosed an optically corrected shield having spherical inner and outer surfaces that defined an optical center C over the bridge of the nose. The thickness of the shield tapers in all directions away from the optical center C, which is the thickest portion of shield. As shown in Table I of that patent, the lens can have a small amount of minus power (±0.03 diopters), and minimizes viewing distortion. Since the optical centerline of this spherical lens is through the optical center C, the optical centerline is spaced from and parallel to the normal (straight ahead) line of sight, as in the Rayton patent.
In the 1980s, the Foster Grant Company sold dual lens Eyeguard protective eyewear, having a spherical lens in front of each eye with both wrap and pantoscopic tilt. As in the Rayton patent, the optical axis of each lens is spaced from and maintained parallel to the straight-ahead/normal line of sight. The optical centerline is horizontally and vertically offset from, as well as parallel to, the normal line of sight. The horizontal and parallel offset of these lines helps neutralize the distortion caused by lateral wrap of the lens, while the vertical and parallel offset helps neutralize the distortion caused by pantoscopic tilt.
A similar “optically corrected” face shield lens is shown in U.S. Pat. No. 6,010,217 which issued to Oakley, Inc. This patent discloses a face shield having a spherical lens in which the optical centerline is horizontally and vertically spaced from and substantially parallel to the normal line of sight when the shield is worn. The optical axis of these shields passes through the apex of the shield, which is the forwardmost point of the shield in the as worn condition. Hence the optical center of the shield is at the apex. This is the same approach that was disclosed by Montesi as early as 1981.
U.S. Pat. Nos. 5,815,848 and 6,038,705 also issued to Oakley, and disclose a low power “optically correct” face shield having a thickest portion at the center of the lens, from which the lens tapers in all directions, as in Montesi's U.S. Pat. No. 4,271,538. This design was also used in visors of military helmets during the 1980s.
A variety of eyewear designs have also been proposed to address the visual demands of particular sports. U.S. Pat. No. 5,614,964 discloses dual lens eyewear, especially adapted for cycling and alpine skiing, in which each lens has an exterior lens surface with a single center of curvature. The inner radius of curvature of each of the right and left lenses is greater than the outer radius of curvature. The centers of curvature of the inner spheres are also offset horizontally and vertically.
U.S. Pat. No. 5,457,502 discloses eyeglasses particularly suited for a person who is bending forward and looking ahead, such as a bicyclist. An upper spherical portion of the lens has a different radius of curvature than the lower spherical portion of the lens, to enhance visual clarity when the cyclist is leaning forward and looking up.
U.S. Pat. No. 5,555,038 also shows spherical lenses for use in eyewear. The centers of curvature of the right and left lenses are horizontally separated by a distance of 0.1 to about 4.0 cm. This geometry is said to help ensure that the lenses fit closely over each eye without distorting or blocking vision of the wearer in the central portion of the lens.